• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
JDBC
 

JDBC

on

  • 273 views

 

Statistics

Views

Total Views
273
Views on SlideShare
273
Embed Views
0

Actions

Likes
0
Downloads
12
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    JDBC JDBC Presentation Transcript

    • Java II--Copyright © 2001-2004 Tom Hunter
    • Java II--Copyright © 2001-2004 Tom Hunter Chapter 18 JDBC
    • Java II--Copyright © 2001-2004 Tom Hunter Background: databases
    • Java II--Copyright © 2001-2004 Tom Hunter • Types of databases --Hierarchical --Relational --Object Relational Background: databases
    • Java II--Copyright © 2001-2004 Tom Hunter • Types of databases --Hierarchical-the first database, invented by IBM, called IMS. Background: databases
    • Java II--Copyright © 2001-2004 Tom Hunter • Types of databases --Relational-the most common, invented by IBM but first marketed by Oracle. Examples: Oracle DB2 Sybase Access* Background: databases
    • Java II--Copyright © 2001-2004 Tom Hunter • Types of databases --Object Relational-uncommon, attempts to place objects in the database. Background: databases
    • Java II--Copyright © 2001-2004 Tom Hunter Relational Databases
    • Java II--Copyright © 2001-2004 Tom Hunter Relational Databases: Entity Integrity • Unit of the Table, smallest unit in a relational database • For a table to be useful, it must enforce Entity Integrity. Entity Integrity—each row in a table can be located by using its Primary Key. 1st Law of Relational Databases Each row in a table must have an attribute(s) that uniquely locates one row. Values in this attribute must be unique. 2nd Law of Relational Databases The primary key attribute(s) cannot contain a null value
    • Java II--Copyright © 2001-2004 Tom Hunter Relational Databases: Entity Integrity • Here is a sample table, USER ID LastName FirstName Age 1 Jones Sam 32 2 Jones Angela 27 3 Smith Ann 22 4 Doe Jack 44 Primary Key—must uniquely identify a row. No nulls allowed.
    • Java II--Copyright © 2001-2004 Tom Hunter Relational Databases: Entity Integrity • Here is another sample table, CODE Code Message A Bill Paid B Bill Overdue C Account written off D Account closed Primary Key—must uniquely identify a row. No nulls.
    • Java II--Copyright © 2001-2004 Tom Hunter Relational Databases: Referential Integrity • A “foreign key” is when the primary key of one table is repeated in a second table as a non primary key. • Using foreign keys, or “referential integrity” allows us to link tables. 3rd Law of Relational Databases If you link two tables with a foreign key, any values present in the foreign-key attribute column must link back to existing primary-key values. 4th Law of Relational Databases It is okay for a foreign key column to contain nulls.
    • Java II--Copyright © 2001-2004 Tom Hunter ID LastName FirstName Age 1 Jones Sam 32 2 Jones Angela 27 3 Smith Ann 22 4 Doe Jack 44 Relational Databases: Referential Integrity ID LastName FirstName Age Code 1 Jones Sam 32 A 2 Jones Angela 27 B 3 Smith Ann 22 A 4 Doe Jack 44 This is the primary key for another table. This column can contain nulls. However, any values present must exist in the table that is referred to. This is a “foreign key”.
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics: Structure of a SQL Statement • When accessing a relational database, you must use the “Structured Query Language” (SQL) • Several types of SQL: queries—for asking questions updates—for making changes insert—for adding new data DDL—for creating tables
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics: Structure of a SQL Statement • Queries: SELECT statements SELECT columns FROM table; Or if we wish not to select all columns: SELECT columns FROM table WHERE expression
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics: Structure of a SQL Statement • Queries: SELECT statements SELECT FirstName, LastName FROM USER WHERE ID = 2;
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics: Structure of a SQL Statement • Updates: UPDATE statements UPDATE table SET column = value; Example: UPDATE table SET LastName = ‘Jones’ WHERE ID = 2;
    • Java II--Copyright © 2001-2004 Tom Hunter SQL Basics: Structure of a SQL Statement • Insert: INSERT statements INSERT INTO table VALUES(values); Example: INSERT INTO USER VALUES( ‘6’, ‘Anderson’, ‘Joe’, 44, ‘A’)
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Connection
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Connection • The first step toward connecting to a database is getting a database connection. • Before you can get a connection, you need a database driver. • The driver makes the connection between a particular database and our Java program. • These drivers are individual to each vendor’s database.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Connection • To make sure your driver is available, you use the following: Class.forName( “sun.jdbc.odbc.JdbcOdbcDriver” ); • The above statement will merely ensure that the Java class containing the driver is available to our program.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Connection • The statement below results in a connection to the database. import java.sql.Connection; … Connection con = DriverManager.getConnection( url, user, pass ); • To create a connection using this method, it is necessary to pass three arguments to the method: username password url
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: url • The Url is a special string of characters that finds the database. • Here is a sample Url: url = jdbc:oracle:thin:@myhostname:1521:OurDB jdbc:oracle:thin:@ —This is database specific myhostname —This is the name of the host where the database is located. 1521 —This is the port on the host where the database is listening. OurDB —This is the name of the database.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Connection • The DriverManager is convenient but not scalable. import java.sql.Connection; … Connection con = DriverManager.getConnection( url, user, pass ); • Once you have opened a connection to the database, you must realize this is a resource. • You mustYou must closeclose the connection you opened.the connection you opened.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Statements • After you have a connection, you need to create a statement. • There are three alternatives, each with plusses and minuses. Statement—used for a query that will be executed once. PreparedStatement—used for a query that will be executed multiple times CallableStatement—used for a query that executes a stored procedure.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: Statement • The Statement object is the easiest to work with. • The Statement object is the least efficient. String query = “SELECT * FROM MYTABLE WHERE ID = 2”; Connection con = DriverManager.getConnection( url, user, pass ); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( query );
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: PreparedStatement • The PreparedStatement object requires more work. • The PreparedStatement object is the most efficient. • The query contains a question mark that is replaced. String query = “SELECT * FROM MYTABLE WHERE ID = ?”; Connection con = DriverManager.getConnection( url, user, pass ); PreparedStatement pstmt = con.prepareStatement( query ); pstmt.setString( 1, 494 ); ResultSet rs = pstmt.executeQuery(); This line substitutes 494 for the first question mark in the query.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: CallableStatement • The CallableStatement object is only appropriate for calling a stored procedure. • The syntax of how you call the stored procedure is database specific. String call = “{ call myProcdure }”; Connection con = DriverManager.getConnection( url, user, pass ); CallableStatement cstmt = con.prepareCall( call ); ResultSet rs = cstmt.executeQuery();
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: ResultSet • The ResultSet object receives the results of the query. String query = “SELECT COL1, COL2 FROM MYTABLE WHERE ID = 2”; Connection con = DriverManager.getConnection( url, user, pass ); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( query ); while( rs.next() ) { String myCol1 = rs.getString( “COL1” ); String myCol2 = rs.getString( “COL2” ); } next() returns true while there are results These correspond to columns in the original query.
    • Java II--Copyright © 2001-2004 Tom Hunter JDBC Basics: ResultSet • No matter which kind of statement you choose, the ResultSet object is used the same way. • As with the Connection object, you must closeclose your ResultSet!
    • Java II--Copyright © 2001-2004 Tom Hunter try { String output = null; String query = “SELECT username from MYTABLE where pass=‘foo’ ”; Connection con = DriverManager.getConnection( url, us, pass); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( query ); while( rs.next() ) { output = rs.getString( “username” ); } rs.close(); stmt.close(); con.close(); } catch( SQLException sql ) { System.out.println( “Uh oh…” ); } You must close these three items, in the reverse order that you opened them!
    • Java II--Copyright © 2001-2004 Tom Hunter DataSource
    • Java II--Copyright © 2001-2004 Tom Hunter DataSource • As I said, the DriverManager is not the best choice for a production system. It doesn’t scale well. • A better alternative is using a DataSource. • A DataSource offers connection poolingconnection pooling, where new connections are not thrown away but are instead set aside for the next time someone needs a connection.
    • Java II--Copyright © 2001-2004 Tom Hunter DataSource: Need to Lookup in JNDI • To use a DataSource, it is necessary to perform a lookup of the resource in something called JNDI [ JNDI = Java Naming and Directory Interface ] • JNDI stores a list of namesnames that associate with resourcesresources
    • Java II--Copyright © 2001-2004 Tom Hunter DataSource: Need to Lookup in JNDI • First we need to create an InitialContext so we can lookup that DataSource Context ctx = new InitialContext(); String dbJNDI = "java:comp/env/OracleJDBC"; DataSource ds = (DataSource) ctx.lookup( dbJNDI ); Connection con = ds.getConnection(); This is the name I assigned to the DataSource when I created it. Here, I’m just looking it up under the name I stored it
    • Java II--Copyright © 2001-2004 Tom Hunter DataSource:Complexity of setup • Using a DataSource is very valuable because it allows connection pooling. • The downside of using a DataSource is the complexity of its setup. Also, each Application Server vendor has its own unique setup. You will need to learn these*.